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Fomites' Role in Disease Transmission is Still Up for Debate

By Kelly M. Pyrek

The
role fomites play in the transmission of infectious disease is still being
contested in the infection control community, with no conclusive decision
emerging from clinical studies. A fomite is defined as an inanimate object that
serves to transmit an infectious agent from person to person.

According to the work of David J. Weber, MD, MPH, and William A. Rutala,
"The acquisition of nosocomial pathogens depends on a complex interplay of
the host, pathogen and environment."1 Breaches in the host's
skin integrity allow microbes to invade, while microorganisms must be present in
a minimum inoculating dose sufficient to trigger infection, virulence,
infectivity and the ability to produce a latent infection. Nosocomial infections
can result from endogenous or exogenous flora, with the latter often present on
an environmental reservoir or fomite.

In the chain of infection (see "Breaking the Chain of Infection,"
July 2002 Infection Control Today), fomites can serve as the reservoir,
with pathogens being spread from the inanimate environment to an animate
environment (the patient) via the hands of healthcare workers (HCWs).

According to Weber and Rutala, "A key concept in considering the
hospital environment as an infectious hazard for patients is proof of a
causative role of inanimate objects in human disease." They point to
several levels of proof offered by researcher Frank Rhame:2

The organism can survive after inoculation on to the fomite.

The pathogen can be cultured from fomites in use.

The pathogen can proliferate on the fomite.

At least some small part of acquisition of infection cannot be accounted
for by other methods of transmission.

Studies show an association between exposure to the contaminated fomite
and infection.

In an editorial in Infection Control and Hospital Epidemiology, Weber
and Rutala pondered the following: Do patients colonized or infected with VRE
contaminate their environment? What is the role of surface contamination in the
transmission of vancomycin-resistant enterocci (VRE)? Is surface contamination
linked to the transmission of other nosocomial pathogens?3 They
concede that in VRE outbreaks, "It often has been difficult to determine
whether cross-transmission occurred due to contaminated common equipment (e.g.,
stethoscopes), acquisition of transient hand carriage by healthcare personnel
due to direct contact with a colonized or infected patient or acquisition of
transient hand carriage by healthcare personnel due to contact with a
contaminated surface. Cross-transmission of VRE occasionally has been linked to
contaminated medical devices, including an electronic thermometer and a
fluidized bed. Disinfection or removal of the contaminated equipment terminated
the outbreaks."

Survival of the Fittest

Weber and Rutala point to various studies conducted to analyze the survival
rates of enterococci inoculated onto environmental surfaces. Noskin, et al.,4
reported that Enterococcus faecalis survived for five days and Enterococcus
faecium for seven days on countertops. Both species survived on bed rails
for 24 hours without significant die-off, on telephone handpieces for 60
minutes, on the diaphragmatic surface of stethoscopes for 30 minutes and on
gloved and ungloved fingers for at least 60 minutes. Other investigators have
demonstrated survival of VRE for more than three days on inoculated surfaces5
or equipment contaminated by colonized or infected patients.6
Survival of 18 hours on pieces of sterile cotton sheets also has been
demonstrated.7

Contamination of the inanimate environment-especially bed rails, bed sheets
and patient gowns -- has been most closely associated with methicillin-resistant
Staphylococcus aureus (MRSA), C. difficile and
antibiotic-resistant Enterococcus. These microorganisms also have been
found on blood pressure cuffs, dietary trays, intravenous pumps, stethoscopes,
utility room sinks, bathroom doors and a sink drain in a patient room.

VRE has been one of the most studied areas of environmental contamination and
its presence has been detected on the following:9

In a study that appeared in the Lancet in 1996, 12 of 29 ventilated
patients acquired VRE; the resistant strain was isolated from 157 of 1,294
environmental cultures. The study concluded that it is impossible to separate
patient-to-patient transmission via HCWs or the contaminated environment, but
that the latter was not a major source of infection.10

"It will be extremely difficult to disentangle the contributions of the
animate and inanimate reservoirs of VRE in leading to transient hand carriage of
VRE by medical personnel," Weber and Rutala write.11
"Clearly, proper handwashing with an antimicrobial agent before and after
each contact with patients or their immediate environment is crucial in
preventing person-to-person transmission of nosocomial pathogens. Unfortunately,
compliance with CDC handwashing guidelines has been noted in less than one half
of the instances in which it is indicated.12 For this reason,
additional contact precautions have been recommended, including wearing gloves
when entering the rooms of patients with VRE. We believe there is sufficient
evidence to state that inanimate surfaces likely play a role in the transmission
of VRE. Supportive evidence includes environmental cultures demonstrating
widespread surface contamination in rooms of many patients colonized or infected
with VRE and experimental evidence that VRE can survive on environmental
surfaces for hours and that hands can become colonized with VRE via patient or
environmental surfaces."

What infection control experts conclude from these various studies is that
the inanimate environment may contribute to the spread of some pathogens such as
VRE, but that the precise contribution is probably 0 percent to less than 25
percent. It has been found that non-critical surfaces play a minor role in the
transmission of most pathogens, although surface contamination may occur with
some pathogens and hands may become colonized. Most experts believe that
meticulous disinfection and handwashing can prevent most transmission of
disease.13

"Even though surface contamination may play a role in disease
transmission, changes in routine disinfection only are unlikely to reduce
disease transmission because recontamination of the patient environment likely
is rapid," Weber and Rutala write.14 "Preliminary studies
suggest that current protocols for terminal cleaning may not eliminate VRE from
environmental surfaces.15 In conclusion, we believe that widespread
environmental contamination with VRE is likely in the rooms of colonized or
infected patients. Good handwashing and use of recommended barrier precautions
are indicated to prevent cross-transmission of VRE. There is no evidence that
changing routine cleaning protocols is likely to alter the level of surface
contamination. However, terminal cleaning protocols may need to be altered.
Research efforts should focus on improving compliance by healthcare providers
with currently recommended handwashing and barrier precautions."

The Role of Surveillance in Environmental Reservoirs

Most infection control experts do not believe routine microbiologic
surveillance of the inanimate hospital environment is warranted. "Although
many epidemics of nosocomial infections have stemmed from reservoirs of
pathogens in the inanimate hospital environment, the contribution of the
environment to the acquisition and spread of endemic nosocomial infections has
been thought to be insignificant," Rutala says.16

In 1974 the Committee on Infections Within Hospitals of the American Hospital
Association concluded, "The occurrence of nosocomial infection has not been
related to levels of microbial contamination of air, surfaces and fomites ...
meaningful standards for permissible levels of such contamination do not exist
... routine environmental microbiologic sampling programs done with no specific
epidemiologic goal in mind are unnecessary and economically unjustifiable."17

Despite this guidance, a nationwide survey of hospital to infection control
programs in 1976-1977 revealed 70 percent of respondents were conducting
moderate to extensive microbiologic surveillance of hospital environments
routinely.18

To test the relationship between environmental contamination and nosocomial
infections, healthcare professionals launched a study of the University of
Wisconsin Hospital that moved from a 56-year-old building into a new and more
spacious facility.19 Cultures of fomites and surfaces (including sink
drains, faucets and inner walls of ice machines) water and air were taken in the
old and new hospitals immediately before taking occupancy and after 6 to 12
months of occupancy.

The most common nosocomial pathogens, including ancinetobacter species,
Enterobacteria and Staphylococcus aureus, were isolated from 17 percent
of 276 specimens obtained from the old hospital and in 14 percent of 311
cultures from the new hospital immediately before occupancy. After 6 to 12
months of occupancy, 11.3 percent of the 311 cultures from the new hospital
yielded common pathogens. Acinetobacter was recovered from cultures in the old
hospital but was found infrequently in the new facility. Pseudomonas also was
recovered frequently from cultures in the old hospital, particularly from sink
drains. Staphylococcus aureus was recovered from both facilities almost
equally. The study closely watched the nosocomial infections among patients
before and after the move and concluded that there was no decline in the rate of
infection immediately after moving into the new hospital's supposed "less
contaminated" environment.

According to the study's researchers, "Despite major differences in
environmental contamination between the old and new hospitals, the incidence of
nosocomial infection in patients remained unchanged. We conclude that organisms
in the inanimate hospital environment contribute negligibly to endemic
nosocomial infection and that routine microbiologic surveillance of the
inanimate environment is not cost effective."20

The study suggests that the increase in environmental contamination in the
new hospital after occupancy can be attributed to organisms originating in the
human environment of the hospital-from infected patients and from the hands of
HCWs. At any time, at least 40 percent of HCWs carry gram-negative bacilli and
10 percent carry Staphylococcus aureus.21

So, is it a chicken-and-egg scenario? Is bacteria transferred onto the hands
from fomites or vice versa? One of the badges of a healthcare professional is a
pager, a fomite waiting for an opportunistic bacteria. Curious about the role
pagers play in the transmission of infection, researchers Deepjot Singh, MD,
Hanspreet Kaur, MD, William Gardner, MD and Lisa B. Treen, BSMT, assessed the
bacterial contamination of pagers in a large community teaching hospital and
level I trauma center.22

One hundred healthcare workers whose pagers were cultured included house
staff, attending physicians, registered nurses, respiratory therapists and
several medical students. In the survey, participants were asked about their
service assignments, how often they cleaned their pagers, what cleaning agents
were used and the time interval since the last cleaning. Pagers were removed
from their cases and their fronts and four sides were each pressed into agar
plates. Pagers were then cleaned with a 70 percent isopropyl alcohol swab and
allowed to dry. Cultures were then repeated.

Queries about HCWs' cleaning practices revealed 88 of 100 participants had
never cleaned their pagers, and two HCWs had cleaned their pagers more than once
in the previous six months. None of the participants reported cleaning their
pagers in the two weeks prior to the study. Those who cleaned their pagers
regularly used an alcohol swab.

Culture results revealed that bacterial counts were highest for respiratory
therapists and lowest for house staff. Medical students had the lowest bacterial
counts, however, they represented just three of the 100 participants. The
bacterial carriage rates were highest on pagers carried by HCWs in the emergency
department and healthcare personnel from the intensive care unit (ICU) had a
significantly higher bacterial load than those in a general medical unit.

All pagers revealed the presence of coagulase-negative staphylococci and Staphylococcus
aureus; other organisms found included Bacillus species, Streptococcus
species and Candida species. Three pagers belonging to house staff grew
methicillin-resistant Staphylococcus aureus (MRSA). Gram-negative bacilli
and enterococci were not found on any of the pagers. The study found that
cleaning the pagers with alcohol resulted in a 94 percent decrease in the total
bacterial colony count and completely eliminated Staphylococcus aureus.

The study conducted by Singh, et al., acknowledges other studies pointing to
stethoscopes, electronic thermometers and otoscopes as potential vectors of
nosocomial infections. One study demonstrated the transfer of Micrococcus
luteus from inoculated stethoscopes to skin and suggested that other
bacteria could be transferred in this manner.23-24 Another study
revealed that staphylococcal species were isolated from 21 percent of
stethoscopes in a hospital setting.25

It has been documented that 22 percent of HCWs cleaned their stethoscopes
regularly.26 This study was conducted in a 450-bed general hospital
to evaluate the bacterial contamination of stethoscopes, determine bacterial
survival on stethoscope membranes and study the efficacy of 70 percent alcohol
or liquid soap for membrane disinfection. Among the 355 stethoscopes tested, 234
carried at least two different bacterial species and 31 carried potentially
pathogenic bacteria. Although some bacteria deposited onto membranes could
survive 6 to 18 hours, none survived after disinfection.

The pager study revealed one common thread in so many studies of the
environment as potential vector: gram-negative bacilli and enterococci were not
isolated from fomites because they require a warm, moist environment. Devices
such as pagers and stethoscopes may not be environments conducive to the growth
of gram-negative bacilli. The study did not assess viral contamination, which
the researchers acknowledge may be transmitted by fomites.27

The researchers concluded: "Hospital pagers are rarely cleaned and are
often touched during or after the examination of patients, without handwashing.
Our study suggests that pagers can be contaminated with potential pathogens,
including antibiotic-resistant strains, and that simple cleaning with 70 percent
isopropyl alcohol significantly decreases bacterial load, including pathogenic
bacteria. However, their role as vectors of nosocomial infection remains
unproved."